Family: Cerambycidae

About the Soybean Stem Borer

Reproduction and Life Cycle

Female soybean stem borers will place their eggs individually on different host plants, often from June to August, which is when the adults are active. If they lay their eggs on a soybean plant, they are often placed in the leaf stalk that the adult chews into. This often wilts the plant and leaves behind a red coloured scar. When the eggs hatch, the larvae will begin feeding within the stalk, and eventually make their way to the plants main stem. The larvae go through 4 instars; each stage will continue to tunnel within the plant. Due to the fact that the larvae eat one another, there will only be 1 larva to survive each plant. This pest overwinters as larvae at the plant stems base. They will pupate in the beginning of the summer, with adults emerging later in June. The soybean stem borer only has one generation annually.

Soybean Stem Borer Identification and Habitat

Identification

The soybean stem borer is considered a long-horned beetle. The adult is 12mm long with a gray body. They have antennae that extend to be longer than their body that are striped black and gray. The larvae are off-white to yellow and are legless. They are also about 12mm long but can reach 16mm at full maturity. They have an accordion-like body shape related to how the segments are attached; the segments grow wider near the head and narrow at the tail. The eggs are tiny and white.

Habitat

While the soybean stem borer prefers soybeans, they will also feed on a number of other plants such as sunflowers, broadleaf weeds, and cocklebur. This pest is common throughout North America. When the larvae tunnel through the leaf stalk and stem, you will notice leaf tissue above the tunnel will wilt and eventually die. If you notice a single dead leaf on a plant that is healthy otherwise, this is an early sign of infestation. You can open the stem to look for this pest. The fully matured larvae will girdle the stem in preparation to overwinter. This will weaken the stem and can cause it to lodge or break. Girdling will have a greater effect on plant varieties that mature early, and lodging tends to be worse with soybean plants that were planted early. Tunneling can often cause up to 7 percent damage to the crops yield.

Soybean Stem Borer Management and Control Methods

Cultural Control

There are numerous prevention methods that can help suppress this pest. While there are currently no soybean products resistant to the soybean stem borer, you can plan to have an early harvest. This has proved to greatly reduce losses caused by lodging. Plow in the fall to keep overwintering survival rates to a minimum. Plowing that places plant residue at least 2 inches beneath the surface is advised. Keep weeds under control in and around your fields so this pest does not have additional host plants to feed on. Also, products that are soybean cyst nematode resistant can help reduce the chance of lodging. Rows that are narrowly spaced (7 to 15 inches) can also help keep lodging from being a serious issue as plants can hold one another up. Crop rotation can also help suppress their population as this pest cannot fly long distances and so they are limited to a small area.

Chemical Control

Control can often be difficult with this pest because once larvae begin tunneling inside the plant they are sheltered from any foliar insecticides. It is also important to note that if you apply a foliar insecticide to control adults, it can lead to a spider mite or aphid outbreak. Also, often times several foliar insecticide applications must be completed to minimize the adult population, which is not usually justified economically. The only time this would be warranted is if loss from lodging was significant and it was a late harvest.

Latin / Alternative Soybean Stem Borer Names

• - Dectes texanus
• - Dectes stem borer

Sources